Wireless test fixtures, when used in combination with in-circuit testers for target printed circuit boards (PCBs), allow for quick and accurate testing of PCBs by providing the necessary electrical and mechanical connections between points of interest on the target PCB with the testing interface of the particular tester being used. A simplified diagram of one such wireless fixture 100 is shown in FIG. 1. A target PCB 105, typically populated with electronic components 107, is held in a stable fashion by a target board support 130. A plurality of probes 135 make contact at one end with points of interest on the target PCB 105 to be tested. The other end of each probe 135 makes contact with electrical contact points on one side of a fixture PCB 110. On the opposite side of the fixture PCB 110 are another set of electrical contact points, each of which is associated with a pin 120. The pins 120 are utilized to connect various points of the fixture PCB 110, with a testing interface 115 of the tester, shown without detail in FIG. 1.
Thus, the fixture PCB 110 is employed as a way of mechanically customizing the testing interface 115 for any particular target PCB 105. Typically, significant forces are applied to one or both sides of the fixture PCB 110 by way of the probes 135 and the pins 120. To prevent inordinate flexing of the fixture PCB 110 under such forces, structural elements, such as spacers 140 and fixture adapter 125, are employed. These structural elements may predominantly reside on the upper or lower side, or both, of the fixture PCB 110.
Some such structural elements may make direct contact with the fixture PCB 110 over a significant portion of the fixture PCB 110. For example, the fixture adapter 125 may contain a number of holes (not shown in FIG. 1) through which the pins 120 protrude to make contact with the fixture PCB 110. Areas of the top of the fixture adapter 125 not occupied by the pins 120 therefore make direct contact with the fixture PCB 110 to provide mechanical support. In other wireless test fixture designs, a structural element may reside atop the fixture PCB 10, making direct contact with much of the top side of the fixture PCB 110 for support.
Unfortunately, such contact has been shown to cause problems when changes to the connections embodied in the fixture PCB 110 are required. These changes are often necessitated by modifications in test strategy, causing a change in the number of points of interest to be checked or a modification in how the points of interest are tested. Also, design modifications made to the target PCB 105 may cause a change of location in the points of interest on the target PCB 105. As a result of these modifications, commensurate changes in the location or number of the probes 135, or in how the probes 135 are connected to the pins 120, are required. In such cases, changes in the electrical connections implemented within the fixture PCB 110 are necessary.
The changes in the fixture PCB 110 are normally implemented in part by way of one or more standard, round, insulated wires, such as small-gauge wire-wrap wires. With respect to the wireless fixture 100, such wires, when residing on the bottom side of the fixture PCB 110, are compressed between the fixture PCB 110 and the fixture adapter 125, potentially causing bending of the fixture PCB 110. For variants of test fixtures with structural elements in contact with the top of the fixture PCB 110, wire-wrap wires existing on the top of the fixture PCB 110 would create similar problems. If the fixture PCB 110 is not maintained sufficiently flat within certain limits, the probes 135 and pins 120 may not make sufficient contact with the fixture PCB 110 in the proper locations, causing undesirable disconnections between the testing interface 115 and the target PCB 105. Also, physical damage to the wires implementing the changes may occur. Such damage is exacerbated in situations where two of the wires cross, as the insulation between the two wires may be compromised, causing a short circuit between those wires.
The wires also potentially cause obstruction of the points on the fixture PCB 110 at which the probes 135 and the pins 120 make contact. This problem may be remedied by gluing the wires to the side of the fixture PCB 110 to restrict the movement of the wires, but such a task is rather time-consuming.
Therefore, from the foregoing, a new structure and method that allows for low-profile, low-movement implementations of circuit changes on a printed circuit board would be advantageous.
Embodiments of the present invention, to be discussed in detail below, represent a structure and method that allow circuit changes to be made to a printed circuit board that occupy an insignificant amount of space above the board, and are essentially stationary. Where two previously unconnected points on a side of the printed circuit board must be connected, electrically conductive tape is applied to the side of the printed circuit board to define a contiguous path between the two points.
Electrically conductive tape is often backed with an adhesive, thus restricting the movement of the tape when applied to the board with the adhesive. Also, conductive tape is typically quite thin compared to the type of wire normally used for such PCB circuit changes, thus occupying less space above the board compared to that wire so that mechanical tolerance problems due to bending of the printed circuit board are significantly reduced.
Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.